116 PLATE XL VI. 



ters of the sponge in a very satisfactory manner. 

 Natural size. 



Fig. 9. One of the semi-spinous, attenuato-acuate, 

 skeleton spicnla. X 250 linear. 



Fig. 10. An atteniiato-acuate, entirely- spined, in- 

 ternal, defensive spiculum. X 250 linear. 



Fig. 11. One of the slender, cylindrical, tension 

 spicula. X 250 linear. 



Fig. 12. A bidentate, inequi-anchorate, retentive 

 spiculum, from the dermal membrane. X 530 

 linear. 



Fig. 13. A dentate-palmate, inequi-anchorate, re- 

 tentive spiculum, from the interstitial membranes. 

 X 530 linear. This form of spiculum was not ob- 

 served in the specimen of the sponge first examined. 

 In the specimen figured they are about equal in 

 number to the bidentate spicula. 



Figs. 14, 15.- - Bipocillated anch orate, retentive 

 spicula, from, the interstitial membranes. X 530 

 linear. These singular forms of spicula are repre- 

 sented on a larger scale from the same species of 

 sponge in plate v, figs. 123 127, vol. i, ' Mon. Brit. 

 Spongiadas.' 



Since the first publication of H. Hyndmani I have 

 received numerous specimens on the shells of Pecten 

 opercularis, but it is only on comparatively a few of 

 them that the sponge is developed in the massive 

 state represented at a a, fig. 7. On by far the 

 greater number of the shells it forms only a thin crust, 

 as represented covering the remaining portions of the 

 shell. 



HALICHONDRIA PULGHELLA, Bowerbank. 



Vol. ii, p. 256, ' Mon. Brit. Spongiadae.' 



Fig. 1 6. - - Represents the type-specimen in the 

 cabinet of the Rev. A. M. Norman. Natural size. 

 Fig. 17. One of the subfusiformi, cylindrical, ter- 



